Low profile illumination in an optical fingerprint sensor

ABSTRACT

An optical fingerprint sensor includes: cover glass for receiving a finger; a transparent electrode layer below a bottom surface of the cover glass; an organic light emitting diode layer (OLED) below the transparent electrode layer; and a metal electrode layer below the OLED layer. Multiple openings extend through each of the transparent electrode layer, OLED layer, and metal electrode layer, and transmit reflected light reflected from a top surface of the cover glass when a finger is positioned over the top surface of the cover glass. A collimator or pinhole filter is below the metal electrode layer, and includes multiple apertures for transmitting the reflected light after the reflected light is transmitted through the multiple openings. An imager is below the bottom surface of the collimator or pinhole filter, and includes an array of pixels that detects the reflected light after the reflected light is transmitted through the multiple apertures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. non-provisionalpatent application Ser. No. 14/871,810, filed on Sep. 30, 2015, whichclaims the benefit of U.S. provisional patent application No.62/111,012, filed on Feb. 2, 2015, and U.S. provisional application No.62/111,022, filed on Feb. 2, 2015.

FIELD

This disclosure generally relates to optical sensors and, moreparticularly, to small size optical fingerprint sensors.

BACKGROUND

Biometric recognition systems are used for authenticating and/orverifying users of devices incorporating the recognition systems.Biometric sensing technology provides a reliable, non-intrusive way toverify individual identity for recognition purposes.

Fingerprints, like various other biometric characteristics, are based ondistinctive personal characteristics and, thus, are a reliable mechanismfor recognizing an individual. There are many potential applications forutilization of fingerprint sensors. For example, fingerprint sensors maybe used to provide access control in stationary applications, such assecurity checkpoints. Electronic fingerprint sensors may also be used toprovide access control in mobile devices, such as cell phones, wearablesmart devices (e.g., smart watches and activity trackers), tabletcomputers, personal data assistants (PDAs), navigation devices, andportable gaming devices. Accordingly, some applications, in particularapplications related to mobile devices, may require recognition systemsthat are both small in size and highly reliable.

Most commercially available fingerprint sensors are based on optical orcapacitive sensing technologies. Unfortunately conventional opticalfingerprint sensors are too bulky to be packaged in mobile devices andother common consumer electronic devices, confining their use to dooraccess control terminals and similar applications where sensor size isnot a restriction. As a result, fingerprint sensors in most mobiledevices are capacitive sensors having a sensing array configured tosense ridge and valley features of a fingerprint. Typically, thesefingerprint sensors either detect absolute capacitance (sometimes knownas “self-capacitance”) or trans-capacitance (sometimes known as “mutualcapacitance”). In either case, capacitance at each pixel in the arrayvaries depending on whether a ridge or valley is present, and thesevariations are electrically detected to form an image of thefingerprint.

While capacitive fingerprint sensors provide certain advantages, mostcommercially available capacitive fingerprint sensors have difficultysensing fine ridge and valley features through large distances,requiring the fingerprint to contact a sensing surface that is close tothe sensing array. As a result, it remains a significant challenge for acapacitive sensor to detect fingerprints through thick layers, such asthe thick cover glass (sometimes referred to herein as a “cover lens”)that protects the display of many smartphones and other mobile devices.To deal with this drawback, a cutout is often formed in the cover glassin an area beside the display, and a discrete capacitive fingerprintsensor (often integrated with a mechanical button) is placed in thecutout area so that it can detect fingerprints without having to sensethrough the cover glass. Unfortunately, the need for a cutout makes itdifficult to form a flush surface on the face of device, detracting fromthe user experience. Also, the existence of mechanical buttons takes upvaluable device real estate.

SUMMARY

One aspect of the disclosure provides an optical fingerprint sensor,comprising: a cover glass comprising a top surface and a bottom surfaceopposite to the top surface, wherein the top surface of the cover glassis configured to receive a finger; a transparent electrode layerpositioned below the bottom surface of the cover glass; an organic lightemitting diode (OLED) layer positioned below the transparent electrodelayer, wherein the OLED layer is configured to emit an illuminationlight beam towards the top surface of the cover glass when the finger ispositioned on the top surface of the cover glass, and wherein the OLEDlayer is configured to emit the illumination light beam through thetransparent electrode layer and through the cover glass layer; a metalelectrode layer positioned below the OLED layer, wherein the metalelectrode layer comprises an opening configured to transmit a reflectedlight beam that is reflected from the top surface of the cover glasswhen the finger is positioned on the top surface of the cover glass; acollimator filter positioned below the metal electrode layer, whereinthe collimator filter comprises a top surface and a bottom surfaceopposite to the top surface, wherein the collimator filter comprises anaperture extending from the top surface of the collimator filter to thebottom surface of the collimator filter, wherein the aperture isconfigured to transmit the reflected light beam after the reflectedlight beam is transmitted through the opening of the metal electrodelayer, wherein the collimator filter comprises an intermediate surfacebetween the top surface of the collimator filter and the bottom surfaceof the collimator filter, wherein the intermediate surface of thecollimator filter is configured to block a stray light beam that isreflected from the top surface of the cover glass when the finger ispositioned on the top surface of the cover glass, and wherein the straylight beam that is blocked by the intermediate surface of the collimatorfilter has a larger angle from normal, relative to the top surface ofcollimator filter, than the reflected light beam that is transmittedthrough the aperture of the collimator filter; and, an imager positionedbelow the bottom surface of the collimator filter, wherein the imagercomprises a pixel configured to detect the reflected light beam afterthe reflected light beam is transmitted through the aperture of thecollimator filter.

Another aspect of the disclosure provides an optical fingerprint sensor,comprising: a cover glass comprising a top surface and a bottom surfaceopposite to the top surface, wherein the top surface of the cover glassis configured to receive a finger; a transparent electrode layerpositioned below the bottom surface of the cover glass; an organic lightemitting diode (OLED) layer positioned below the transparent electrodelayer, wherein the OLED layer is configured to emit illumination lighttowards the top surface of the cover glass when the finger is positionedover the top surface of the cover glass, wherein the OLED layer isconfigured to emit the illumination light through the transparentelectrode layer and through the cover glass layer; a metal electrodelayer positioned below the OLED layer; a plurality of openings extendingthrough the transparent electrode layer, through the OLED layer, andthrough the metal electrode layer, wherein the plurality of openings areconfigured to transmit reflected light that is reflected from the topsurface of the cover glass when the finger is positioned over the topsurface of the cover glass; a collimator filter positioned below themetal electrode layer, wherein the collimator filter comprises aplurality of apertures configured to transmit the reflected light afterthe reflected light is transmitted through the plurality of openings;and, an imager positioned below the bottom surface of the collimatorfilter, wherein the imager comprises an array of pixels configured todetect the reflected light after the reflected light is transmittedthrough the plurality of apertures of the collimator filter.

Yet another aspect of the disclosure provides an optical fingerprintsensor, comprising: a cover glass comprising a top surface and a bottomsurface opposite to the top surface, wherein the top surface of thecover glass is configured to receive a finger; a transparent electrodelayer positioned below the bottom surface of the cover glass; an organiclight emitting diode (OLED) layer positioned below the transparentelectrode layer, wherein the OLED layer is configured to emitillumination light towards the top surface of the cover glass when thefinger is positioned over the top surface of the cover glass, whereinthe OLED layer is configured to emit the illumination light through thetransparent electrode layer and through the cover glass layer; a metalelectrode layer positioned below the OLED layer; a plurality of openingsextending through the transparent electrode layer, through the OLEDlayer, and through the metal electrode layer, wherein the plurality ofopenings are configured to transmit reflected light that is reflectedfrom the top surface of the cover glass when the finger is positionedover the top surface of the cover glass; a collimator filter or pinholefilter positioned below the metal electrode layer, wherein thecollimator filter or pinhole filter comprises a plurality of aperturesconfigured to transmit the reflected light after the reflected light istransmitted through the plurality of openings; and, an imager positionedbelow the bottom surface of the collimator filter or pinhole filter,wherein the imager comprises an array of pixels configured to detect thereflected light after the reflected light is transmitted through theplurality of apertures of the collimator filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a device that includes anoptical sensor and a processing system according to an embodiment of thedisclosure.

FIG. 2 illustrates an example of a mobile device that includes anoptical sensor according to an embodiment of the disclosure.

FIG. 3 illustrates an example of an optical sensor with a collimatorfilter layer according to an embodiment of the disclosure.

FIG. 4 illustrates an example of light interacting with an opticalsensor having a collimator filter layer according to an embodiment ofthe disclosure.

FIG. 5 illustrates an alternative embodiment of a collimator filterlayer according to an embodiment of the disclosure.

FIG. 6 illustrates an example of an optical sensor with a collimatorfilter layer and OLED illumination layer according to an embodiment ofthe disclosure.

FIG. 7 illustrates an example of an OLED illumination layer and acollimator filter structure according to an embodiment of thedisclosure.

FIG. 8 illustrates a method of imaging an input object according to anembodiment of the disclosure.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Turning to the drawings, and as described in greater detail herein,embodiments of the disclosure provide methods and systems to opticallyimage an input object such as a fingerprint. In particular, a method andsystem is described wherein an optical sensor includes a collimatorfilter layer which operates as a light conditioning layer, interposedbetween a light illumination layer and an image sensor array.Transmitted light from the illumination layer reflects from an inputobject in a sensing region above a cover layer. The reflected light isfiltered by the collimator filter layer such that only certain of thereflected light beams reach optical sensing elements in the image sensorarray.

Employing the collimator filter layer of the present disclosure preventsblurring while allowing for a lower-profile image sensor, such as afingerprint sensor, than is possible with purely lens-based or pinholecamera based imaging sensors. Thus, the image sensor can be made thinfor use in mobile devices such as cell phones. Placing individualcollimator apertures over each optical sensing element, or group ofelements, provides better sensitivity than purely pinhole based imagersby transmitting more light to the optical sensing elements. The presentdisclosure describes the use of the collimator filter layer to enableoptical sensing through a large range of thicknesses of cover layers.

FIG. 1 is a block diagram of an example of an electronic device 100 thatincludes an optical sensor device 102 and a processing system 104,according to an embodiment of the disclosure. By way of example, basicfunctional components of the electronic device 100 utilized duringcapturing, storing, and validating a biometric match attempt areillustrated. The processing system 104 includes a processor(s) 106, amemory 108, a template storage 110, an operating system (OS) 112, and apower source(s) 114. Each of the processor(s) 106, the memory 108, thetemplate storage 110, and the operating system 112 are interconnectedphysically, communicatively, and/or operatively for inter-componentcommunications. The power source 114 is interconnected to the varioussystem components to provide electrical power as necessary.

As illustrated, processor(s) 106 are configured to implementfunctionality and/or process instructions for execution withinelectronic device 100 and the processing system 104. For example,processor 106 executes instructions stored in memory 108 or instructionsstored on template storage 110 to identify a biometric object ordetermine whether a biometric authentication attempt is successful orunsuccessful. Memory 108, which may be a non-transitory,computer-readable storage medium, is configured to store informationwithin electronic device 100 during operation. In some embodiments,memory 108 includes a temporary memory, an area for information not tobe maintained when the electronic device 100 is turned off. Examples ofsuch temporary memory include volatile memories such as random accessmemories (RAM), dynamic random access memories (DRAM), and static randomaccess memories (SRAM). Memory 108 also maintains program instructionsfor execution by the processor 106.

Template storage 110 comprises one or more non-transitorycomputer-readable storage media. In the context of a fingerprint sensor,the template storage 110 is generally configured to store enrollmentviews for fingerprint images for a user's fingerprint or otherenrollment information. More generally, the template storage 110 may beused to store information about an object. The template storage 110 mayfurther be configured for long-term storage of information. In someexamples, the template storage 110 includes non-volatile storageelements. Non-limiting examples of non-volatile storage elements includemagnetic hard discs, solid-state drives (SSD), optical discs, floppydiscs, flash memories, or forms of electrically programmable memories(EPROM) or electrically erasable and programmable (EEPROM) memories,among others.

The processing system 104 also hosts an operating system (OS) 112. Theoperating system 112 controls operations of the components of theprocessing system 104. For example, the operating system 112 facilitatesthe interaction of the processor(s) 106, memory 108 and template storage110.

According to various embodiments, the processor(s) 106 implementhardware and/or software to obtain data describing an image of an inputobject. The processor(s) 106 may also align two images and compare thealigned images to one another to determine whether there is a match. Theprocessor(s) 106 may also operate to reconstruct a larger image from aseries of smaller partial images or sub-images, such as fingerprintimages when multiple partial fingerprint images are collected during abiometric process, such as an enrollment or matching process forverification or identification.

The processing system 104 includes one or more power sources 114 toprovide power to the electronic device 100. Non-limiting examples ofpower source 114 include single-use power sources, rechargeable powersources, and/or power sources developed from nickel-cadmium,lithium-ion, or other suitable material as well power cords and/oradapters which are in turn connected to electrical power.

Optical sensor device 102 can be implemented as a physical part of theelectronic device 100, or can be physically separate from the electronicdevice 100. As appropriate, the optical sensor device 102 maycommunicate with parts of the electronic device 100 using any one ormore of the following: buses, networks, and other wired or wirelessinterconnections. In some embodiments, optical sensor device 102 isimplemented as a fingerprint sensor to capture a fingerprint image of auser. In accordance with the disclosure, the optical sensor device 102uses optical sensing for the purpose of object imaging including imagingbiometrics such as fingerprints. The optical sensor device 102 can beincorporated as part of a display, for example, or may be a discretesensor.

Some non-limiting examples of electronic devices 100 include personalcomputers of all sizes and shapes, such as desktop computers, laptopcomputers, netbook computers, tablets, web browsers, e-book readers, andpersonal digital assistants (PDAs). Additional example electronicdevices 100 include composite input devices, such as physical keyboardsand separate joysticks or key switches. Further example electronicdevices 100 include peripherals such as data input devices (includingremote controls and mice) and data output devices (including displayscreens and printers). Other examples include remote terminals, kiosks,video game machines (e.g., video game consoles, portable gaming devices,and the like), communication devices (including cellular phones, such assmart phones), and media devices (including recorders, editors, andplayers such as televisions, set-top boxes, music players, digital photoframes, and digital cameras).

The optical sensor device 102 may provide illumination to the sensingregion. Reflections from the sensing region in the illuminationwavelength(s) are detected to determine input information correspondingto the input object.

The optical sensor device 102 may utilize principles of directillumination of the input object, which may or may not be in contactwith a sensing surface of the sensing region depending on theconfiguration. One or more light sources and/or light guiding structuresmay be used to direct light to the sensing region. When an input objectis present, this light is reflected from surfaces of the input object,which reflections can be detected by the optical sensing elements andused to determine information about the input object.

The optical sensor device 102 may also utilize principles of internalreflection, which includes total internal reflection (TIR) and non-TIRinternal reflection (collectively Fresnel reflections), to detect inputobjects in contact with a sensing surface. One or more light sources maybe used to direct light in a light guiding element at an angle at whichit is internally reflected at the sensing surface of the sensing region,due to different refractive indices at opposing sides of the boundarydefined by the sensing surface. Contact of the sensing surface by theinput object causes the refractive index to change across this boundary,which alters the internal reflection characteristics at the sensingsurface, causing light reflected from the input object to be weaker atportions where it is in contact with the sensing surface. Highercontrast signals can often be achieved if principles of frustrated totalinternal reflection (FTIR) are used to detect the input object. In suchembodiments, the light may be directed to the sensing surface at anangle of incidence at which it is totally internally reflected, exceptwhere the input object is in contact with the sensing surface and causesthe light to partially transmit across this interface. An example ofthis is presence of a finger introduced to an input surface defined by aglass to air interface. The higher refractive index of human skincompared to air causes light incident at the sensing surface at thecritical angle of the interface to air to be partially transmittedthrough the finger, where it would otherwise be totally internallyreflected at the glass to air interface. This optical response can bedetected by the system and used to determine spatial information. Insome embodiments, this can be used to image small scale fingerprintfeatures, where the internal reflectivity of the incident light differsdepending on whether a ridge or valley is in contact with that portionof the sensing surface.

FIG. 2 illustrates an example of an electronic device 116, such as amobile phone, which includes cover glass 118 over a display 120. Thedisclosed method and system may be implemented by using the display 120as the optical sensor to image an input object. Alternatively, aseparate discrete component 122 provides the optical sensingcapabilities. A discrete sensor may provide more flexibility indesigning the optical components of the sensor for optimum illuminationand/or signal conditioning than when attempting to integrate the opticalsensor components on a display substrate, such as a TFT (thin-filmtransistor) backplane.

FIG. 3 illustrates an example of a stack-up for an optical image sensordevice 200 used to image an object 216, such as a fingerprint. Thesensor device 200 includes an image sensor array 202, a collimatorfilter layer or light conditioning layer 204 disposed above the imagesensor array 202, an illumination layer 207 disposed above thecollimator filter layer 204, a light source 208, and a cover layer 210.In certain embodiments, a blocking layer 214 may also be provided.

The cover layer 210 protects the inner components of the sensor device200, such as the image sensor array 202. The cover layer 210 may includea cover glass or cover lens that protects inner components of a displayin addition to the sensor device 200. A sensing region for the inputobject is defined above the cover layer 210. A top surface 218 of thecover layer 210 may form a sensing surface, which provides a contactarea for the input object 216 (e.g., fingerprint). The cover layer 210is made of any material such as glass, transparent polymeric materialsand the like.

Although generally described in the context of fingerprint forillustrative purposes, the input object 216 is any object to be imaged.Generally, the input object 216 has various features. By way of example,the input object 216 has ridges and valleys. Due to their protrudingnature, the ridges contact the sensing surface 218 of the cover 210layer. In contrast, the valleys do not contact the sensing surface 218and instead form an air gap between the input object 216 and the sensingsurface 218. The input object 216 may have other features, such asstain, ink, and the like that do not create significant structuraldifferences in portions of the input object 216, but which affect itsoptical properties. The methods and systems disclosed herein aresuitable for imaging such structural and non-structural features of theinput object 216.

The illumination layer 207 includes a light source 208 and/or a lightguiding element 206 that directs illumination to the sensing region inorder to image the input object 216. As shown in FIG. 3, the lightsource 208 transmits beams or rays of light 212 into the light guidingelement 206 and the transmitted light propagates through the lightguiding element 206. The light guiding element 206 may utilize totalinternal reflection, or may include reflecting surfaces that extractlight up towards the sensing region. Some of the light in theillumination layer 207 may become incident at the sensing surface 218 inan area that is contact with the input object 216. The incident light isin turn reflected back towards the collimator filter layer 204. In theexample shown, the light source 208 is disposed adjacent to the lightguiding element 206. However, it will be understood that the lightsource 208 may be positioned anywhere within the sensor 200 providedthat emitted light reaches the light guiding element 206. For example,the light source 208 may be disposed below the image sensor array 202.Moreover, it will be understood that a separate light guiding element206 is not required. For example, the light transmitted from the lightsource 208 can be transmitted directly into the cover layer 210 in whichcase the cover layer 210 also serves as the light guiding element. Asanother example, the light transmitted from the light source 208 can betransmitted directly to the sensing region, in which case the lightsource 208 itself serves as the illumination layer.

A discrete light source is also not required. For example, the methodand system contemplate using the light provided by a display or thebacklighting from an LCD as suitable light sources. The light providedby the illumination layer 207 to image the object 216 may be in nearinfrared (NIR) or visible. The light can have a narrow band ofwavelengths, a broad band of wavelengths, or operate in several bands.

The image sensor array 202 detects light passing through the collimatorfilter layer 204. Examples of suitable sensor arrays are complementarymetal oxide semiconductor (CMOS), charge coupled device (CCD) sensorarrays, and thin film sensor arrays. The sensor array 202 includes aplurality of individual optical sensing elements capable of detectingthe intensity of incident light.

To achieve optical sensing of fingerprints and fingerprint-sizedfeatures through thicker cover layers 210, light reflected from thefingerprint is conditioned by the light collimator filter layer 204 sothat the light reaching a sensing element in the image sensor array 202comes only from a small spot on the input object 216 directly above thesensor element. In the absence of such conditioning, any light arrivingat a sensing element from a region on the object far away from theoptical sensing elements contributes to image blurring.

To condition the light in accordance with the disclosure, the collimatorfilter layer 204 is provided with an array of apertures, or collimatorholes, 220 with each aperture being directly above one or more opticalsensing elements on the image sensor array 202. The apertures 220 areformed using any suitable technique, such as laser drilling, etching andthe like.

The collimator filter layer 204 only allows light rays reflected fromthe input object 216 (e.g., finger) at normal or near normal incidenceto the collimator filter layer 204 to pass and reach the optical sensingelements of the image sensor array 204. In one embodiment, thecollimator filter layer 204 is an opaque layer with array of holes 220.The collimator filter layer 204 is laminated, stacked, or built directlyabove the image sensor array 202. By way of example, the collimatorfilter layer 204 may be made of plastics such as polycarbonate, PET,polyimide, carbon black, inorganic insulating or metallic materials,silicon, or SU-8. In certain embodiments, the collimator filter layer204 is monolithic.

Also shown in FIG. 3 is blocking layer 214, which is optionally providedas part of optical sensor 200. The blocking layer 214 is asemitransparent or opaque layer that may be disposed above thecollimator filter layer 204. By way of example, the blocking layer 214may be disposed between the cover layer 210 and the illumination layer207, as shown in FIG. 3. Alternatively, the blocking layer 214 may bedisposed between the illumination layer 207 and the collimator filterlayer 204. In either case, the blocking layer 214 obscures components ofthe sensor device 200, such as the apertures in the collimator filterlayer 204, from ambient light illumination, while still allowing thesensor device 200 to operate. The blocking layer 214 may include of anumber of different materials or sub-layers. For example, a thin metalor electron conducting layer may be used where the layer thickness isless than the skin depth of light penetration in the visible spectrum.Alternately, the blocking layer 214 may include a dye and/or pigment orseveral dyes and/or pigments that absorb light, for example, in thevisible spectrum. As yet another alternative, the blocking layer 214 mayinclude several sub-layers or nano-sized features designed to causeinterference with certain wavelengths, such as visible light forexample, so as to selectively absorb or reflect different wavelengths oflight. The light absorption profile of the blocking layer 214 may beformulated to give a particular appearance of color, texture, orreflective quality thereby allowing for particular aesthetic matching orcontrasting with the device into which the optical sensor device 200 isintegrated. If visible illumination wavelengths are used, asemitransparent layer may be used to allow sufficient light to passthrough the blocking layer to the sensing region, while stillsufficiently obscuring components below.

FIG. 4 illustrates a closer view of the collimator filter layer 204disposed between the illumination layer 207 and the image sensor array202 and interaction of light within the sensor device 200. Portions 226of the cover layer 210 are in contact with ridges of the input object216 and portion 228 of the cover layer 210 is in contact with air due tothe presence of a valley of object 216. Image sensor array 202 includesoptical sensing elements 230, 232, 234 and 236 disposed below aperturesor holes 220 of the collimator filter layer 204.

Illustratively shown are a series of light rays reflected at the coverlayer 210. For example, light rays 238 reflect from the cover layer 210at portions occupied by ridges or valleys of the object 216. Because thelight rays 238 are above collimator apertures 220 and are relativelynear normal, the light rays 238 pass through the apertures 220 in thecollimator filter layer 204 and become incident on optical sensingelements 232 and 236, for example. The optical sensing elements can thenbe used to measure the intensity of light and convert the measuredintensity into image data of the input object 216. On the other hand,light beams 240 and 242, which have a larger angle from normal, strikethe collimator filter layer 204, either on its top surface or at surfacewithin the aperture (e.g., aperture sidewall) and are blocked andprevented from reaching optical sensing elements in the image sensorarray 202.

A metric of the collimator filter layer 204 is an aspect ratio of theapertures or holes 220. The aspect ratio is the height of the holes(“h”) 244 in the collimator filter layer 204 divided by hole diameter(“d”) 246. The aspect ratio should be sufficiently large to prevent“stray” light from reaching the optical sensing elements directly undereach collimator hole. An example of stray light is light ray 242reflected from portion 228 of the cover layer 210 (e.g., a valley),which would reach sensing elements underneath a ridge in the absence ofthe collimator filter layer. Larger aspect ratios restrict the lightacceptance cone to smaller angles, improving the optical resolution ofthe system. The minimum aspect ratio can be estimated using a ratio ofthe distance from the collimator filter layer 204 to the object beingimaged (e.g., finger) divided by the desired optical resolution of thefinger. In some embodiments, the collimator apertures 220 arecylindrical or conical in shape. The sidewalls of the collimatorapertures 220 may include grooves or other structures to prevent straylight from reflecting off the walls and reaching the optical sensingelements. The effective aspect ratio is determined by the average holediameter along height of the collimator holes. Examples of suitableaspect ratios are ratios in the range of about 3:1 to 100:1 and moretypically in the range of about 5:1 to 20:1.

It is generally desirable to make the height of the holes 244 of thecollimator apertures 220 as thin as possible to provide the mostflexibility for fabricating the collimator filter layer 204 andintegrating it with the underlying image sensor array 202, such as aCMOS or CCD image sensor. A small aperture diameter 246 may be used tomaintain the desired collimator aspect ratio. However, if the apertureis made too small (less than a few times the wavelength of light beingused), diffraction effects can contribute to additional blurring as thelight rays exiting the collimator apertures 220 diverge. Suchdiffraction effects can be mitigated by placing the collimator filterlayer 204 as close to the image sensor array 202 as possible, ideallymuch closer than the Fraunhofer far field distance (i.e., r²/lambda,where r is the aperture radius and lambda is the light wavelength).

It is also generally desirable to minimize the distance between thecollimator filter layer 204 and the image sensor array 202 to allow thelight reaching the optical sensing elements of the image sensor array202 to be as concentrated as possible. In addition, if this sensor array202 to collimator filter layer 204 distance is too large, stray lightfrom adjacent holes may reach a particular optical sensing element,contributing to image blurring.

If the image sensor array 202 is a CCD or CMOS image sensor, where theoptical sensing element pitch (distance between elements) may be smallerthan the collimator hole pitch (distance between holes), the lightpassing through a single collimator aperture 220 may illuminate morethan one optical sensing element. Such an arrangement is shown byoptical sensing elements 234 and 236 in FIG. 4. In such cases, theprocessing system (see FIG. 1) may combine the light intensity recordedby all the optical sensing elements corresponding to a given collimatoraperture. The resulting fingerprint image after processing raw data fromthe image sensor array 202 may have a resolution corresponding to thearray of collimator apertures. It will be noted that the arrangement ofapertures 220 in the collimator filter layer 204 may result in someoptical sensing elements in the sensor array 202 going unused. Examplesof an unused optical sensing elements are sensing elements 240. Becauseoptical sensing elements 240 are not underneath a collimator hole,reflected rays will be blocked before reaching them. Image processingmay remove the unused sensor elements and scale the image appropriatelybefore the data is used in image reconstruction or image matching, forexample.

The imaging resolution (in dpi) of the optical sensor 200 is defined bythe resolution of the apertures 220 in the collimation filter layer 204whereas the pitch is the distance between each aperture. In the opticalsensor 200, each aperture 220 in the collimator filter layer 204corresponds to a sample of a feature of the object 216 being imaged,such as a sample from a ridge or valley within a fingerprint. Tomaximize resolution, the sampling density (which is equal to theaperture density) should be large enough such that multiple samples aretaken of each feature of interest. Thus, for example, to image ridges ina fingerprint, the pitch may be on the order of 50 to 100 microns sincethe pitch of the ridges themselves is on the order of 150 to 250microns. If it desired to capture more granular features, such as poresin a fingerprint, a smaller pitch such as 25 microns would beappropriate. Conversely, a larger pitch can be used to capture largerfeatures of the input object.

The optical sensor 200 performs similarly over a wide range of distancesbetween the collimator filter layer 204 and the sensing surface 220because the filtering of reflected light is generally thicknessindependent, as long as the aspect ratio of the holes in the collimatorfilter layer 204 is chosen to support the desired optical resolution.

FIG. 5 shows an alternative embodiment of the collimator filter layer204. As described above, the collimator filter layer 204 is made oflight-absorbing materials and includes an array of apertures 220. In thealternative embodiment shown, the top surface of the collimator filterlayer 204 further includes a reflecting layer 250. The reflecting layer250 allows light beams that would normally be absorbed by the collimatorfilter layer 204 to be reflected back upwards towards the sensingregion. Redirecting the light back to the sensing region allows thereflected light to be recycled so that some of the recycled light can bereflected off the input object to be imaged and transmitted through thecollimator filter layer apertures.

Inclusion of the reflecting layer 250 minimizes light loss by reflectingthe stray light back to the input object 216 without requiring a highlevel of illumination in the overall sensor package. The top of thelight-absorbing collimator filter layer body may be roughened usingvarious texturizing techniques, including but not limited to,sandblasting, coating with fillers, UV embossing or dry etching. Thisroughened top may then covered with a thin layer of metal, which createsa surface that is multifaceted in a randomized fashion. The reflectinglayer 250 may be made of any suitable material that will reflect lightsuch as aluminum, chromium, and silver to name a few examples.

The method and system disclosed contemplate various ways to include thecollimator filter layer 204 into the overall structure of the opticalsensor device 200. For example, the collimator filter layer 204 may be apre-patterned structure that is laminated or stacked onto the imagesensor array 202, as generally depicted in FIGS. 3-4. Alternativeembodiments are contemplated by the present disclosure. For example, onealternative embodiment is to pattern or create the collimator filterlayer 204 directly onto a CMOS image sensor die or wafer, as generallydepicted in FIG. 5. For example, a wafer-level collimator layer may beformed by micro-fabrication. Instead of placing a separate collimatorfilter layer 204 on top of the image sensor array 202, back-endprocesses are added to CMOS image sensor array fabrication. With thistechnique, no separate manufacturing of the collimator filter layer isrequired. On top of the CMOS image sensor array, liquid-type polymerresin with light-absorbing dyes such as carbon black may be coated firstthen cured to form the collimator filter layer body. After the polymerresin is cured, metal may be optionally sputtered onto the cured resintop to act as a reflective layer. The aperture pattern may be madethrough photolithography and etching of the metal and the polymer layerunderneath subsequently to create the apertures. As a final step, themetal layer can be roughened to create a reflecting/diffusing layer.

In yet another embodiment, the collimator filter layer 204 is replacedor supplemented with an optical interference filter that blocks “stray”light at angles of incidence that are relatively far from normal to theimaging plane. Multilayer optical filters can be used that transmitlight at incidence near normal in much the same way such a filter can beconstructed to only transmit light at specific wavelengths. Althoughsuch an angle-specific filter may be designed to work for specific lightwavelengths, such an interference filter may be used to reject the straylight coming from adjacent ridges and valleys.

The collimator filter layer 204 may also be a transparent glasscollimator filter with round openings on top and bottom. This type ofcollimator filter layer is made using double-sided alignment techniqueto create top and bottom openings that are aligned, but withoutphysically hollow holes through the glass body. The top surface of thecollimator filter layer can be textured to be a diffuser for the lightentering while the bottom surface can be metallic to recycle byreflecting the light back to the transparent glass body. One of theadvantages is that this method makes lamination simpler since there areno physically hollow apertures. With this glass collimator filter layer,cover glass, light guide film, and glass filter can be laminated withreadily available lamination equipment.

In some embodiments, an opaque glass collimator filter with drilledapertures can be used. This is similar to the previously describedcollimator filter film. The manufacturing method may be the same, exceptfor the fact that the body is glass. The aperture density is determinedbased on the required dpi.

FIGS. 6-7 depict ways to illuminate the underside of a finger (or otherobject) placed on the cover glass of a mobile electronics device so thatan optical fingerprint imager integrated with the light source canacquire an image of the fingerprint. Integrating an OLED light sourceabove an image sensor provides both the illumination and pinhole orcollimator array useful for a low profile lens-less fingerprint imagingdevice.

With both collimator and pinhole type low profile (lens-less) imagers,there is very little distance available between the imaging componentsand the cover glass below the object (finger) being imaged. It istherefore difficult to uniformly illuminate the surface of the finger.One solution is to place a light guide between the imager and the finger(or the cover glass) into which light is injected from the side, andfeatures patterned/etched/molded on the underside of the light guidereflect or scatter light up toward the finger to illuminate it. However,it can be difficult to uniformly illuminate the finger in this manner,and a light source (typically LED) often needs to be attached to theside of the light guide.

Constructing a thin film OLED lighting source that sits on the topsurface of the collimator/pinhole array provides a few advantages overthe light guide approach: 1) The OLED light source can be much thinnerthan a typical light guide with its attached light source; 2) Becauselight can be generated over the entire area, except for the lightconditioning layer apertures/holes (see FIG. 7), it is much easier touniformly illuminate the object being imaged; 3) It may be possible tointegrate the OLED illumination layers directly on the collimatorstructure, eliminating the need to align the light source to thecollimator.

FIG. 6 depicts an example of an optical fingerprint sensor 600 with anOLED illumination layer in cross section view. The optical fingerprintsensor 600 is configured to image a fingerprint of a finger 216 providedon or over a top surface 218 of a cover glass 210. As shown in FIG. 6,the illumination layer includes an OLED stack 607 a-c positioned below abottom surface 619 of the cover glass 210, opposite to the top surface218 that provides an input surface for the finger 216. The OLED stack607 a-c includes a transparent electrode layer 607 a made of indium tinoxide (ITO) positioned below the bottom surface 619 of the cover glasslayer 210. While ITO is an ideal choice of conductive material for theupper transparent electrode layer 607 a due to its conductiveproperties, transparency, and manufacturability, it will be understoodthat any other suitable transparent conductor may be used instead ofITO, provided that the chosen transparent conductor allows theillumination light 212 to pass through to the sensing region above. Anorganic light emitting diode (OLED) layer 607 b is positioned below thetransparent electrode layer 607 a. The OLED layer 607 b includes anemissive organic layer that emits illumination light 212 of the desiredwavelength(s) towards the top surface 218 of the cover glass 210 duringfingerprint sensing. A metal electrode layer 607 c is provided below theOLED layer 607 b. The metal electrode layer 607 b may be made of anysuitable metal conductor and does not need to be transparent.

A collimator filter layer 204 is provided below the metal electrodelayer 607 c. The collimator filter layer 204 includes a plurality ofcollimator holes or apertures 220 configured to transmit reflected light238 that is reflected from top surface of the cover glass when thefinger 216 is positioned on the top surface. The collimator structure204 and corresponding apertures 220 can be configured as describedabove. In particular, similar to as shown and described with respect toFIG. 4 above, the collimator holes 220 transmit reflected light 238 thatis within an acceptance angle from normal incidence to the collimatorfilter 204 (e.g., relative to a plane defined by the top surface of thecollimator filter). As shown in FIG. 6, the normal of the collimatorfilter 204 may coincide with the normal of the top surface 218 of thecover glass 218. Interior surfaces within the collimator apertures(e.g., sidewalls and/or other intermediate surfaces), block stray lightthat falls outside of the acceptance angle with respect to normalincidence, thereby limiting the light detected by the imager 202 andimager pixels 230 to within an acceptance angle determined by thecollimator structure 204. In FIG. 6, a gap is shown between a bottomsurface of the collimator filter structure 204 and a top surface of theimager 202 and imager pixels 230; however, it is understood that thisgap may be omitted and the collimator filter structure 204 may bepositioned directly on top of the imager 202 (e.g., through wafer levelfabrication as described above with respect to FIG. 5).

As shown in FIG. 6, the transparent electrode layer 607 a, OLED layer607 b, and metal electrode layer 607 c may each include openings inareas corresponding to the collimator holes 220 to allow reflected light238 from the finger 216 to pass through and be detected by the imagerpixels 230 below. FIG. 6 also shows light paths for the illuminationlight beams 212 and the reflected light beams 238 during operation ofthe sensor 600 for fingerprint imaging. During operation, a voltage isapplied across the OLED layer 607 b by the electrode layers 607 a, 607c, causing the OLED layer 607 b to emit an illumination light beam 212through the upper transparent electrode layer 607 a and through thetransparent cover glass layer 210, towards the finger 216 that ispositioned on the upper surface 218 of cover glass. The illuminationlight beam 212 is then reflected from the finger 216 (at the top surfaceof the cover glass), and this reflected light beam 238 is transmittedback through the cover glass layer 210, after which it is transmittedthrough the openings in the illumination layers 607 a-c. Since the metalelectrode layer 607 c is provided below the OLED layer 607 b that emitsthe illumination light 212 upwards towards the finger 216, the metalelectrode need not be transparent, provided that it includes openingsthat allow the reflected light 238 to pass through to the collimatorholes 220 below. After passing through the opening in the metalelectrode layer 607 c, the reflected light beam 238 is transmittedthrough a collimator aperture 220 if it is within the acceptance angledetermined by the aperture geometry, whereas an intermediate surface inthe collimator aperture 220 (e.g., a sidewall or other surface betweenthe top surface and the bottom surface of the collimator filter) blocksa stray light beam that is outside of an acceptance angle from normal(see, e.g., FIG. 4). After passing through the collimator aperture 220,the reflected light beam 238 is detected by a pixel 230 of the imager202.

A plurality of collimator apertures 220 and a plurality of openings inOLED stack 607 a-c can be used to capture multiple spots on the finger216. FIG. 6 depicts an example of spacing between collimator holes 220relative to a spacing between fingerprint ridges on a finger 216. As canbe seen in FIG. 6, which shows only one fingerprint ridge and onefingerprint valley on the finger 216 but multiple collimator apertures220, the spacing between collimator apertures 220 can be smaller than aspacing between fingerprint ridges in order to sufficiently sample thefingerprint. It will be appreciated that the exact dimensions can varydepending on the implementation.

FIG. 7 depicts an example of an OLED illumination layer and collimatorstructure in top view (plan view). The sensor has a collimator filterlayer 204 that includes collimator holes 220 to allow light transmitthrough to an imager (not shown). The areas corresponding to thecollimator holes 220 are free of the OLED light emitting layer 607 b toallow light reflected the finger to pass through the OLED layer 607 bbefore passing through the collimator holes 220. In FIG. 7, both theopenings in the OLED layer 607 b and the openings in the collimatorfilter layer 204 are arranged in a regular array and aligned to eachother, although other patterns are possible.

The OLED illumination layer may be deposited on top of the pinhole orcollimator substrate (Collimator/Substrate 204 in FIG. 6). This can bedone after the holes are formed in the substrate as long as thepatterning for all of the OLED stack layers is done by shadow masking orprinting rather than subtractive wet chemical processing.

Alternatively, it may be possible to deposit one large OLED device overthe substrate before the holes are formed, as long as forming the holesin the substrate (and OLED layers) does not impair the OLED optical orelectrical performance.

The entire pinhole/collimator substrate could be covered by a singleOLED device, or the OLED could be separated into individual pixels thatare driven/addressed passively or with direct connections.

Rather than constructing the OLED stack on the pinhole/collimatorsubstrate, the OLED stack could be made on a separate piece of glass orplastic (or any other transparent material), or even on the underside ofthe cover glass in the case of a mobile electronics device such as acell phone or tablet. In this case, the OLED device fabricated on aseparate substrate could still have the same hole pattern as the lightconditioning layer, and these holes could be aligned to the holes in thepinhole/collimator substrate during assembly so that light reflectedfrom the finger can travel through the apertures to the underlyingimager.

If the OLED stack is fabricated on a transparent substrate, thecollimator structures could then be deposited on top of the OLED stack(while leaving the same holes open), so that when the transparentsubstrate is inverted, the collimator structures would also beintegrated on the OLED substrate, removing the need for a separatepinhole/collimator structure that must be aligned to the OLEDstructures. In this case, the “Collimator/Substrate” structures depictedin FIG. 6 could be deposited after the OLED stack is deposited on theglass (or “Cover glass” 210 in FIG. 6).

The light provided by the illumination layer to sense the finger may bein near infrared (NIR). It can be in the visible as well. Note that itcan have a narrow band of wavelengths, a broad band of wavelengths, oroperate in several bands.

FIG. 8 shows a method 800 of imaging in accordance with the presentdisclosure.

In step 802, the sensing region is illuminated using an illuminationlayer having a light source and/or light guiding element. As previouslydescribed, this may be done by using a light source directing light intoa separate light guiding element or by transmitting light directly intothe cover layer. The transmitted light is directed towards a sensingregion above the cover layer and reflected from the object towards thelight collimator layer.

In step 804, some of the reflected light is blocked at the collimatorfilter layer while other light passes through apertures in thecollimator filter layer. Generally, light rays at relatively near normalincidence to the collimator filter layer will pass through the apertureswhile light rays further from normal incidence will be blocked. Lightmay be blocked by the top surface of the collimator layer, anintermediate layer of the collimator, a bottom layer of the collimator,or sidewalls of the collimator aperture.

In step 806, the light which passes through the collimator filter layerbecomes incident on one or more optical sensing elements on the sensorarray below the light collimator layer. In instances where more than onesensing element is below a particular aperture in the collimator filterlayer, the detected light at the sensing elements may be averaged orotherwise combined. The image data may be adjusted to account forsensing elements that are not below an aperture.

In step 808, the detected light at the image sensor array is processedto form an image or a partial image of the input object. Such processingmay include, for example, stitching partial images together, relatingvarious partial images to one another in a template, and/or comparingcaptured image data to previously stored image data as part of anidentification or verification process.

Although this invention describes optical object imaging in the contextof fingerprint image sensing, the method and system may be used to imageany object. For example, a high resolution image of a palm or hand maybe acquired by placing the hand directly on the cover layer. Imaging ofnon-biometric objects is also with the scope of this disclosure.

While embodiments of this disclosure have been described with respect tofingerprint sensors, this illumination scheme could be used toilluminate any object that is to be placed directly over a low-profileimaging device that uses arrays of apertures to form its image. Largerimagers could be used to image/scan something larger than a fingerprint,such as an entire hand or palm.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. An optical fingerprint sensor, comprising: a cover glass comprising atop surface and a bottom surface opposite to the top surface, whereinthe top surface of the cover glass is configured to receive a finger; atransparent electrode layer positioned below the bottom surface of thecover glass; an organic light emitting diode (OLED) layer positionedbelow the transparent electrode layer, wherein the OLED layer isconfigured to emit an illumination light beam towards the top surface ofthe cover glass when the finger is positioned on the top surface of thecover glass, and wherein the OLED layer is configured to emit theillumination light beam through the transparent electrode layer andthrough the cover glass layer; a metal electrode layer positioned belowthe OLED layer, wherein the metal electrode layer comprises an openingconfigured to transmit a reflected light beam that is reflected from thetop surface of the cover glass when the finger is positioned on the topsurface of the cover glass; a collimator filter positioned below themetal electrode layer, wherein the collimator filter comprises a topsurface and a bottom surface opposite to the top surface, wherein thecollimator filter comprises an aperture extending from the top surfaceof the collimator filter to the bottom surface of the collimator filter,wherein the aperture is configured to transmit the reflected light beamafter the reflected light beam is transmitted through the opening of themetal electrode layer, wherein the collimator filter comprises anintermediate surface between the top surface of the collimator filterand the bottom surface of the collimator filter, wherein theintermediate surface of the collimator filter is configured to block astray light beam that is reflected from the top surface of the coverglass when the finger is positioned on the top surface of the coverglass, and wherein the stray light beam that is blocked by theintermediate surface of the collimator filter has a larger angle fromnormal, relative to the top surface of collimator filter, than thereflected light beam that is transmitted through the aperture of thecollimator filter; and an imager positioned below the bottom surface ofthe collimator filter, wherein the imager comprises a pixel configuredto detect the reflected light beam after the reflected light beam istransmitted through the aperture of the collimator filter.
 2. Theoptical fingerprint sensor of claim 1, wherein the OLED layer comprisesa plurality of individual pixels.
 3. The optical fingerprint sensor ofclaim 1, wherein the imager comprises a complementary metal oxidesemiconductor (CMOS) image sensor array.
 4. The optical fingerprintsensor of claim 1, wherein the transparent electrode layer comprisesindium tin oxide (ITO).
 5. The optical fingerprint sensor of claim 1,further comprising: a transparent substrate separate from the collimatorfilter, wherein the metal electrode layer, the OLED layer, and thetransparent electrode layer are formed on the transparent substrate. 6.The optical fingerprint sensor of claim 5, wherein the transparentsubstrate comprises plastic.
 7. The optical fingerprint sensor of claim5, wherein the transparent substrate comprises glass.
 8. The opticalfingerprint sensor of claim 1, wherein the collimator filter provides asubstrate, and wherein the metal electrode layer, the OLED layer, andthe transparent electrode layer are formed on the substrate provided bythe collimator filter.
 9. The optical fingerprint sensor of claim 1,wherein the collimator filter comprises a plurality of apertures,wherein the metal electrode layer comprises a plurality of openings, andwherein a spacing between fingerprint ridges of the finger is greaterthan a spacing between the plurality of apertures of the collimatorfilter and greater than a spacing between the plurality of openings ofthe metal electrode layer.
 10. The optical fingerprint sensor of claim1, wherein the collimator filter comprises a plurality of apertures,wherein the metal electrode layer comprises a plurality of openings, andwherein the plurality of apertures of the collimator filter are alignedto the plurality of openings of the metal electrode layer.
 11. Theoptical fingerprint sensor of claim 1, wherein the intermediate surfaceof the collimator filter comprises a sidewall surface of the aperture.12. An optical fingerprint sensor, comprising: a cover glass comprisinga top surface and a bottom surface opposite to the top surface, whereinthe top surface of the cover glass is configured to receive a finger; atransparent electrode layer positioned below the bottom surface of thecover glass; an organic light emitting diode (OLED) layer positionedbelow the transparent electrode layer, wherein the OLED layer isconfigured to emit illumination light towards the top surface of thecover glass when the finger is positioned over the top surface of thecover glass, wherein the OLED layer is configured to emit theillumination light through the transparent electrode layer and throughthe cover glass layer; a metal electrode layer positioned below the OLEDlayer; a plurality of openings extending through the transparentelectrode layer, through the OLED layer, and through the metal electrodelayer, wherein the plurality of openings are configured to transmitreflected light that is reflected from the top surface of the coverglass when the finger is positioned over the top surface of the coverglass; a collimator filter positioned below the metal electrode layer,wherein the collimator filter comprises a plurality of aperturesconfigured to transmit the reflected light after the reflected light istransmitted through the plurality of openings; and an imager positionedbelow the bottom surface of the collimator filter, wherein the imagercomprises an array of pixels configured to detect the reflected lightafter the reflected light is transmitted through the plurality ofapertures of the collimator filter.
 13. The optical fingerprint sensorof claim 12, wherein the OLED layer comprises a plurality of individualpixels.
 14. The optical fingerprint sensor of claim 12, wherein theimager comprises a complementary metal oxide semiconductor (CMOS) imagesensor.
 15. The optical fingerprint sensor of claim 12, wherein thetransparent electrode layer comprises indium tin oxide (ITO).
 16. Theoptical fingerprint sensor of claim 12, further comprising: atransparent piece of glass or plastic separate from the collimatorfilter, wherein the metal electrode layer, the OLED layer, and thetransparent electrode layer are disposed on the transparent piece ofglass or plastic.
 17. An optical fingerprint sensor, comprising: a coverglass comprising a top surface and a bottom surface opposite to the topsurface, wherein the top surface of the cover glass is configured toreceive a finger; a transparent electrode layer positioned below thebottom surface of the cover glass; an organic light emitting diode(OLED) layer positioned below the transparent electrode layer, whereinthe OLED layer is configured to emit illumination light towards the topsurface of the cover glass when the finger is positioned over the topsurface of the cover glass, wherein the OLED layer is configured to emitthe illumination light through the transparent electrode layer andthrough the cover glass layer; a metal electrode layer positioned belowthe OLED layer; a plurality of openings extending through thetransparent electrode layer, through the OLED layer, and through themetal electrode layer, wherein the plurality of openings are configuredto transmit reflected light that is reflected from the top surface ofthe cover glass when the finger is positioned over the top surface ofthe cover glass; a collimator filter or pinhole filter positioned belowthe metal electrode layer, wherein the collimator filter or pinholefilter comprises a plurality of apertures configured to transmit thereflected light after the reflected light is transmitted through theplurality of openings; and an imager positioned below the bottom surfaceof the collimator filter or pinhole filter, wherein the imager comprisesan array of pixels configured to detect the reflected light after thereflected light is transmitted through the plurality of apertures of thecollimator filter.
 18. The optical fingerprint sensor of claim 17,wherein the OLED layer comprises a plurality of individual pixels. 19.The optical fingerprint sensor of claim 17, wherein the transparentelectrode layer comprises indium tin oxide (ITO).
 20. The opticalfingerprint sensor of claim 17, further comprising: a transparent pieceof glass or plastic separate from the collimator filter, wherein themetal electrode layer, the OLED layer, and the transparent electrodelayer are disposed on the transparent piece of glass or plastic.